How wasps saved Asia’s forests (commentary)

In our recent study, we combined field observations and satellite imagery to show how the tiny pest-killing lopezi wasp (Anagyrus lopezi) helped combat deforestation in Thailand, Cambodia, Lao PDR, Myanmar, and Vietnam by controlling a pest that was devastating cassava crops across the region.

The world-hopping lopezi wasp is a beneficial insect whose arrival in Asia restored just one of the many ecological checks and balances that was lost when cassava and pink mealybug went intercontinental.

Conservationists tend to be apprehensive about the use of exotic organisms for biological control — the purposeful and science-guided movement of species to control others. However, as we see with Thailand’s cassava, alien pests generally pose a much greater threat than do their cautiously selected enemies. Unlike the few catastrophes that emanated from misguided introductions in the early 1900s, recent biological control initiatives have been overwhelmingly effective.

This post is a commentary. The views expressed are those of the author, not necessarily Mongabay.

Normally we only hear about the problems and risks of biological control, the use of one introduced organism to manage another. But one inconspicuous insect has accomplished miracles across tropical Asia, slowing deforestation and helping farmers, too.

In our recent study, led by Kris Wyckhuys of the Fujian Agriculture & Forestry University in China, we combined field observations and satellite imagery to show how the tiny pest-killing lopezi wasp (Anagyrus lopezi) helped combat deforestation in Thailand, Cambodia, Lao PDR, Myanmar, and Vietnam by controlling a pest that was devastating cassava crops across the region.

Cassava, also known as manioc and tapioca, is an important crop in the tropics and provides food to an estimated 800 million people across the globe. Cassava has been widely cultivated in Asia for decades. Asian farmers value cassava as a food, animal feed, and source of industrial starch. Based primarily on this crop, Thailand became the world’s largest exporter of starch and its cassava suffered few significant pests — until 2008.

Previously unknown in Asia, the cassava pink mealybug — the villain in our story — was first reported in Thailand in late 2008. It spread across the country and, from 2009 to 2010, Thailand’s cassava production dropped 27 percent due to damage by mealybugs. The country’s cassava sector experienced losses estimated at over half a billion USD. The price of cassava surged 138 to 162 percent and farmers across Asia, especially those not yet impacted, expanded production by over 300,000 hectares (about 741,000 acres) in response to the inflated price. Satellite observations show that, mostly as a result of the expanded cassava production, deforestation increased the subsequent year by 388 percent in Cambodia, 185 percent in Myanmar, 608 percent in Vietnam, and by 330 percent in Lao PDR.

Thailand’s agricultural agencies rapidly sought solutions to their cassava crisis. Attempts to control the spread included burning infested crops and monitoring transported plant material. Insecticide use intensified too. But the most effective intervention was the introduction of the mealybug’s nemesis: the lopezi wasp.

The lopezi wasp life-cycle centers on cassava pink mealybugs. Like the alien monster in some grotesque 1970s sci-fi horror movie — though here the tiny, two-millimeter wasp is the hero, not the villain — the wasp hunts its hapless prey and lays its eggs in them. Once hatched, the larvae devour their mealybug hosts from within, before emerging as adults that stalk more unwary cassava pink mealybugs… and the cycle continues. Nothing distracts the lopezi wasp — it is a single-species assassin.

Brought from Africa, where they had been introduced previously, millions of wasps were mass-reared and released across Thailand in 2010–2011. By 2014 the wasp had spread into 97 percent of mealybug areas across mainland Southeast Asia. Where the wasps went, the cassava yields recovered. The price of cassava stabilized and deforestation slowed. By 2011, we observed that forest loss was lower than 2010 by 42 percent in Cambodia, 32 percent in Vietnam, and 95 percent in Myanmar, with Lao PDR lagging slightly behind with a drop of 51 percent by 2012.

Intercontinental insights

Cassava is associated with around two hundred herbivorous insects worldwide, the vast majority of which don’t pose any pest problems. The world-hopping lopezi wasp is a beneficial insect whose arrival in Asia restored just one of the many ecological checks and balances that was lost when cassava and pink mealybugs went intercontinental.

The South American characters in our story — the cassava, mealybug, and wasp — had met away from home before. The mealybug had arrived in Congo in the 1970s and had found plenty of cassava to fuel its Africa-wide spread. Entomologists scoured South America for wild mealybugs and their natural predators. They found them in Paraguay. Lopezi wasps were dispatched to Benin (following a ‘quarantine stop’ near London) for tests, breeding, and release. Africa’s cassava production recovered by over 90 percent. Unlike our study in Asia, we lack data on how forests were impacted by these events.

A farmer holding cassava, which provides food to an estimated 800 million people across the globe. Photo Credit: CIAT.

Conservationists tend to be apprehensive about the use of exotic organisms for biological control — the purposeful and science-guided movement of species to control others. History and its cane toads, etc., fuels these fears. However, as we see with Thailand’s cassava, alien pests generally pose a much greater threat than do their cautiously selected enemies. Unlike the few catastrophes that emanated from misguided introductions in the early 1900s, recent biological control initiatives have been overwhelmingly effective. These successes are less widely known, though the economic benefits far outweigh the costs. The economic benefits alone — the cost ratio is claimed to be as high as 250:1 (and can even reach >1,000:1) — make biological control a far better choice than pesticides.

Clearly, biological control can benefit conservation. Cassava cultivation was a major driver of deforestation and the lopezi wasp averted this pressure. Without the wasp, farmers would have had to adapt: maybe diversifying to other crops or depending more heavily on pesticides. Our Asian success story was due to the rapid detection and identification of the mealybug and rapid access to a pest-killing wasp. Agencies acted promptly and in close collaboration with the private-sector.

The wasp remains naturalized across tropical Asia (and Africa), impeding further pink mealybug infestations, and has recently been introduced to Java and Sumatra in Indonesia. Mealybugs recently appeared in eastern Indonesia and East Timor – and the lopezi wasp was itching to follow.

Anagyrus lopezi, a millimeter-long wasp that was discovered in 1981 in the Paraguayan Chaco, permanently resolved mealybug pest problems across two continents and averted widespread famine and saved the lives of nearly 20 million people in Africa during the 1980s. Photo Credit: Georg Goergen, IITA.